The equilibrium and dynamic interfacial tension of water/n-octane plus sorbitan monolaurate (the commercial name of Span 20) were measured using the pendant drop technique at four temperatures, (274.2, 278.2, 282.2, and 293.2) K. The concentration range of Span 20 is from (0.014 to 1.41) g.kg(-1). The experimental results showed that Span 20 has excellent interface activity and a pronounced dynamic effect on the water/n-octane interface. The critical micelle concentration of Span 20 at different temperatures was determined, and it shifts toward lower value with the increase of temperature. The dynamic interfacial tension data show that, at the beginning of the adsorption process, it was only diffusion-controlled. At the near-equilibrium stage, there exists an adsorption barrier due to the strong molecular interaction of Span 20,